"Three helicopters were in the air. It was a real snowstorm. Suddenly we heard a bang and someone shouted 'everybody down.' Then there was blood everywhere. Nearby, there was a huge pool of blood," one eyewitness told a German TV station, according to the BBC.

The person killed, who died of his or her injuries on the scene, is understood to have been the pilot of one of the helicopters, according to German media.

Photos showed police and emergency workers clambering over the wreckage, possibly in an attempt to reach someone inside. One police officer appeared to stagger away from the aircraft, helped by colleagues.

The crash occurred as over 400 police officers gathered for a training exercise on how to deal with fan violence at soccer games.

The Berlin state police and prosecutor have opened an investigation into the circumstances of the crash, a spokesperson told Bild.